1. Field of the Invention
The present invention relates to a method of preparing 2-phenyl benzotriazoles which are useful as ultraviolet ray absorbers in plastics, paints, oils and so on, and which are expressed by the following formula I: ##STR3## (wherein R.sub.1 denotes a hydrogen atom, a chlorine atom, a lower alkyl group having 1 to 4 carbon atoms, a lower alkoxyl group having 1 to 4 carbon atoms, a carboxyl group or a sulfonic acid group; R.sub.2 denotes a hydrogen or chlorine atom, a lower alkyl group having 1 to 4 carbon atoms or a lower alkoxyl group having 1 to 4 carbon atoms; R.sub.3 denotes a hydrogen or chlorine atom, an alkyl group having 1 to 12 carbon atoms, a lower alkoxyl group having 1 to 4 carbon atoms, a phenyl group, a phenyl group substituted by an alkyl group having 1 to 8 carbon atoms, phenoxy group or a phenylalkyl group with an alkyl part having 1 to 4 carbon atoms; R.sub.4 denotes a hydrogen or chlorine atom, a hydroxyl group or an alkoxyl group having 1 to 4 carbon atoms; and R.sub.5 denotes a hydrogen atom, an alkyl group having 1 to 12 carbon atoms or a phenylalkyl group with an alkyl part having 1 to 4 carbon atoms).
The present invention particularly relates to a method for preparing 2-phenyl benzotriazoles expressed by Formula I comprising reduction with hydrogen of 2-phenyl benzotriazole-N-oxides expressed by the following formula II: ##STR4## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 each denote the same as in Formula I).
2. Description of the Prior Art
Such 2-phenylbenzotriazoles are generally produced by chemical or electrolytic reduction of o-nitrohydroxy azobenzenes expressed by the following formula III: ##STR5## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 each denote the same as in Formula I). Each of these conventional methods, however, has its own advantages and disadvantages, and is not always completely satisfactory. For example, Japanese Patent Publication No. 5934/1962 and U.S. Pat. No. 3,773,751 disclose a method of preparing 2-phenylbenzotriazoles in a good yield by chemically reducing o-nitroazobenzenes with zinc powder in an alcoholic sodium hydroxide solution. Such a sodium hydroxide-zinc system, however, involves the problem that it produces zinc sludge which causes contamination of waste water, and the disadvantage that the waste produced cannot easily be disposed of.
U.S. Pat. No. 2,362,988 discloses a method which uses as a reductant ammonium sulfide, an alkali sulfide, a zinc-ammonia system, a hydrogen sulfide-sodium system or a zinc-hydrochloric acid system. This method, however, has the disadvantages that a large amount of sulfite or zinc salts is produced, resulting in problems with respect to waste water contamination and difficulty of waste disposal,
Japanese Patent Laid-Open No. 133076/1981 (Chem. Abstr. 88 197149b) discloses a method which uses as a catalyst an aromatic dihydroxy compound or a quinone compound and which also requires as a reductant zinc, ammonium sulfide, an alkali metal sulfide, hydrosulfite or hydrazine. This method also has the above-described problem with respect to waste water containing metals, as well as involving problems with respect to the generation of poisonous gases from sulfide reductants and the toxicity of hydrazine itself.
Japanese Patent Laid Nos. 113974/1977 and 113973/1977 (Chem. Abstr. 88 152408u and 105347p respectively) disclose a method of preparing 2-phenylbenzotriazoles in a good yield by reducing the corresponding o-nitroazobenzenes with hydrogen in the presence of a hydrogenation catalyst and a basic substance. As a result of supplementary studies, however, it has been found that many kinds of impurities are produced in small amounts and cannot be removed by washing the reaction product with methanol and then recrystallizing it with ethanol. This method therefore has the problem that the 2-phenylbenzotriazoles produced by this method are inferior to those available at present in terms of both quality and cost.
Japanese Patent Laid-Open No. 170172/1984 (Chem. Abstr. 102 45959k) and Japanese Patent Laid-Open No. 72682/1998 (U.S. Pat. No. 4,943,637) which are related to this application disclose methods of reducing o-nitroazobenzene derivatives expressed by Formula I with alcohols in basic catalysts using quinones and aromatic ketones, respectively.
These methods are excellent methods which can resolve the problems described above with respect to air pollution and waste water contamination, but they still involve the following disadvantages:
The method disclosed in Japanese Patent Laid-Open No. 72682/1988 which uses aromatic ketones as catalysts exhibits a good yield with the expensive catalyst used but is unsuitable for large-scale production on an industrial scale because heat is rapidly generated during the course of the reaction. The method disclosed in Japanese Patent Laid-Open No. 170172/1984 which uses quinones as catalysts exhibits a relatively good yield but higher costs are involved because the quinones used as catalysts deteriorate and cannot be recovered. This method is also unsuitable for use as an additive in colorless plastics because the resulting products would become strongly tinged with yellow. This tendency is particularly strong in the case where R.sub.3 in Formula II is an alkyl group and R.sub.1, R.sub.2, R.sub.4 and R.sub.5 are each a hydrogen atom.
The applicant has proposed a method of preparing 2-phenylbenzotriazoles expressed by Formula I by reducing 2-phenylbenzotriazole-N-oxides of Formula II or o-nitroazobenzenes of Formula III in the following manner:
(1) reduction with an aldehyde in the presence of an aromatic ketone compound and a base (Japanese Patent-Laid Open No. 21537/1986, Chem. Abstr. 106 176394c);
(2) reduction with a primary or secondary alcohol in the presence of a catalyst comprising an aromatic ketone compound together with a basic compound (Japanese Patent Laid-Open No. 72683/1988, U.S. Pat. No. 4,780,541); or
(3) electrolytic reduction in the presence of an alkali metal hydroxide in water or a mixture of water and, alcohol (Japanese Patent Laid-Open No. 186886/1988, Chem. Abstr. 47417u ).
The applicant has also proposed a method for preparing 2-phenylbenzotriazole expressed by the above-described Formula I by reducing the 2-phenylbenzotriazole-N-oxides with an aldehyde in the presence of a catalyst comprising an aromatic ketone compound with a basic compound (Japanese Patent Laid-Open No. 215379/1986, U.S. Pat. No. 4,780,541).